Quantifying the contribution of three competing pathways to total degradation in groundwater by a triple-isotope analysis approach

Mapping Intimacies ◽

10.5194/egusphere-egu2020-14776 ◽

2020 ◽

Author(s):

Martin Thullner ◽

Florian Centler ◽

Thomas Hofstetter

Keyword(s):

Stable Isotope ◽

Isotope Fractionation ◽

Environmental Science ◽

Isotope Analysis ◽

Enrichment Factors ◽

Theoretical Concept ◽

Degradation Pathways ◽

Theoretical Concepts ◽

Dual Isotope ◽

Stable Isotope Fractionation

In groundwater and other environmental compartments, compound-specific stable isotope analysis (CSIA) has been used for the determination of specific degradation pathways by analyzing the stable isotopes of two elements. This &#8216;dual-isotope&#8217; or two-dimensional isotope&#8217; analysis also allows for an estimation of the contribution of two different pathways contributing both to the overall degradation and stable isotope fractionation. Heterogeneous groundwater flow patterns lead to some yet acceptable uncertainities in the results of this method. &#160;Recent CSIA approaches also allow for investigating the simultaneous stable isotope fractionation effects for three different elements. Such information on the stable isotope fractionation of three different elements of a degradable compound could be used for a quantitative analysis of the contribution of different degradation pathways in systems with three different pathways, but up to know there is no theoretical concepts providing such quantitative estimate.The aim of the present study is to overcome this shortage and to present such theoretical concept for the quantification of single pathway contribution to the overall biodegradation in groundwater and other systems with three parallel degradation pathways. For this purpose the approach of Centler et al. (2013) for the analysis of dual-isotope analysis has been expanded to consider the fractionation of three different elements affected by three different pathways. The obtained analytical expression allows for the quantification of each pathway to total degradation based stable isotope enrichment factors and measured stable isotope signatures. The applicability of the concept is demonstrated using data from Wijker et al. (2013).&#160;Centler, F., Hesse, F., and Thullner, M. (2013) Journal of Contaminant Hydrology, 152, 97-116.Wijker, R. S., Bolotin, J., Nishino, S. F., Spain, J. C., and Hofstetter, T. B. (2013) Environmental Science & Technology, 47, 6872-6883.&#160;

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Reactive transport of dichloromethane in laboratory aquifers: insights from dual-element isotope analysis and biomolecular approaches

10.5194/egusphere-egu2020-15103 ◽

2020 ◽

Author(s):

Maria Prieto Espinoza ◽

Sylvain Weill ◽

Benjamin Belfort ◽

François Lehmann ◽

Jérémy Masbou ◽

...

Keyword(s):

Stable Isotope ◽

Water Table ◽

Isotope Fractionation ◽

Isotope Analysis ◽

Enrichment Factors ◽

Degradation Pathways ◽

Transient Conditions ◽

Mass Removal ◽

Water Table Fluctuations ◽

Over Time

Dichloromethane (DCM) is a toxic industrial solvent frequently detected in multi-contaminated aquifers. DCM often co-occurs with chlorinated ethenes resulting in complex mixtures posing challenges to predict its fate in groundwater. Changes in hydrochemistry and redox conditions in groundwater due to fluctuations in the water table may affect the extent and pathways of pollutant biodegradation. In this context, Compound-Specific Isotope Analysis (CSIA) is a useful tool to evaluate natural degradation of halogenated hydrocarbons. In this study, the impact of water table fluctuations on DCM biodegradation was examined in two laboratory aquifers using dual-element isotope analysis - the stable isotope fractionation of two elements (e.g., 13C and 37Cl), and high-throughput biomolecular approaches. The aquifers were supplied with contaminated groundwater from the former industrial site Thermeroil (France). High-resolution sampling and monitoring of pore water allowed examining, under steady and transient conditions, the aquifers response with respect to hydrochemistry and microbial composition. A dual C-Cl stable isotope approach (&#923;C/Cl = &#916;&#948;13C/&#916;&#948;37Cl) was developed using GC-IRMS (C-DCM) and GC-MS (Cl-DCM) to estimate the extent of DCM degradation and to identify DCM degradation pathways. Under the experimental steady conditions, dissolved oxygen (<1.2 mg/L) and increasing Fe2+ concentrations at lower depths of the aquifer models indicated iron-reducing prevailing conditions, while mass transfer of oxygen increased during water table fluctuations. Pronounced carbon isotope fractionation of DCM was associated with larger DCM mass removal under transient conditions (>90%) compared to steady conditions (mass removal of 35%). Under transient conditions, carbon enrichment factors (&#949;C) became larger over time ranging from -18.9 &#177; 3.4&#8240; to -33 &#177; 0.3&#8240; whereas chlorine enrichment factors (&#949;Cl) remained constant (-3.6 &#177; 0.7&#8240;). In contrast, a similar &#949;C of -20 &#177; 3.5&#8240; (beginning of transient condition) but a larger &#949;Cl of -10.8 &#177; 2&#8240; were determined under steady conditions. As &#923;C/Cl values are independent of complicating masking effects, and thus reflect reaction mechanisms, dual C-Cl isotope plots suggested distinct DCM degradation pathways under steady and transient conditions with &#923;C/Cl values of 1.68 &#177; 0.26 and 3.41 &#177; 0.50, respectively. Even though a contribution of different mechanisms may take place during transient conditions, &#923;C/Cl values fall in the range of SN1 pathways reported for Ca. Dichloromethanomonas elyunquensis (&#923;C/Cl = 3.40 &#177; 0.03).&#160; The distinct &#923;C/Cl values may imply mechanistically distinct C-Cl bond cleavage reactions subjected to microbial adaptations during dynamic hydrogeological conditions. Although bacterial communities did not significantly change over time, the occurrence of Geobacter under both steady and transient conditions supports DCM degradation under iron-reducing prevailing conditions. Altogether, our results highlight that water table fluctuations enhance DCM biodegradation and influence DCM degradation pathways compared to steady conditions. This integrative study provides new insights into in situ degradation of DCM in contaminated aquifers and accounts the effects of dynamic water tables on DCM degradation.

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Multi-element (C, H, Cl, Br) stable isotope fractionation as a tool to investigate transformation processes for halogenated hydrocarbons

Environmental Science Processes & Impacts ◽

10.1039/c9em00498j ◽

2020 ◽

Vol 22 (3) ◽

pp. 567-582

Author(s):

Ann Sullivan Ojeda ◽

Elizabeth Phillips ◽

Barbara Sherwood Lollar

Keyword(s):

Stable Isotope ◽

Isotope Fractionation ◽

Isotope Analysis ◽

Halogenated Hydrocarbons ◽

Halogenated Hydrocarbon ◽

Stable Isotope Fractionation ◽

Compound Specific Isotope Analysis ◽

Transformation Processes

A review that highlights the utility of multi-element compound-specific isotope analysis (CSIA) in halogenated hydrocarbon remediation.

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Evaluation of Toluene Degradation Pathways by Two-Dimensional Stable Isotope Fractionation

Environmental Science & Technology ◽

10.1021/es8003415 ◽

2008 ◽

Vol 42 (21) ◽

pp. 7793-7800 ◽

Cited By ~ 85

Author(s):

Carsten Vogt ◽

Esther Cyrus ◽

Ilka Herklotz ◽

Dietmar Schlosser ◽

Arne Bahr ◽

...

Keyword(s):

Stable Isotope ◽

Isotope Fractionation ◽

Degradation Pathways ◽

Two Dimensional ◽

Toluene Degradation ◽

Stable Isotope Fractionation

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Compound-Specific Isotope Analysis of RDX and Stable Isotope Fractionation during Aerobic and Anaerobic Biodegradation

Environmental Science & Technology ◽

10.1021/es8005942 ◽

2008 ◽

Vol 42 (21) ◽

pp. 7772-7777 ◽

Cited By ~ 36

Author(s):

Anat Bernstein ◽

Zeev Ronen ◽

Eilon Adar ◽

Ronit Nativ ◽

Harald Lowag ◽

...

Keyword(s):

Stable Isotope ◽

Isotope Fractionation ◽

Isotope Analysis ◽

Anaerobic Biodegradation ◽

Stable Isotope Fractionation ◽

Compound Specific Isotope Analysis ◽

Aerobic And Anaerobic

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Unravelling the process of petroleum hydrocarbon biodegradation in different filter materials of constructed wetlands by stable isotope fractionation and labelling studies

Biodegradation ◽

10.1007/s10532-021-09942-1 ◽

2021 ◽

Author(s):

Andrea Watzinger ◽

Melanie Hager ◽

Thomas Reichenauer ◽

Gerhard Soja ◽

Paul Kinner

Keyword(s):

Stable Isotope ◽

Constructed Wetlands ◽

Hydrogen Isotope ◽

Petroleum Hydrocarbon ◽

Isotope Fractionation ◽

Isotope Effects ◽

Filter Material ◽

Hydrocarbon Biodegradation ◽

Stable Isotope Fractionation ◽

Filter Materials

AbstractMaintaining and supporting complete biodegradation during remediation of petroleum hydrocarbon contaminated groundwater in constructed wetlands is vital for the final destruction and removal of contaminants. We aimed to compare and gain insight into biodegradation and explore possible limitations in different filter materials (sand, sand amended with biochar, expanded clay). These filters were collected from constructed wetlands after two years of operation and batch experiments were conducted using two stable isotope techniques; (i) carbon isotope labelling of hexadecane and (ii) hydrogen isotope fractionation of decane. Both hydrocarbon compounds hexadecane and decane were biodegraded. The mineralization rate of hexadecane was higher in the sandy filter material (3.6 µg CO2 g−1 day−1) than in the expanded clay (1.0 µg CO2 g−1 day−1). The microbial community of the constructed wetland microcosms was dominated by Gram negative bacteria and fungi and was specific for the different filter materials while hexadecane was primarily anabolized by bacteria. Adsorption / desorption of petroleum hydrocarbons in expanded clay was observed, which might not hinder but delay biodegradation. Very few cases of hydrogen isotope fractionation were recorded in expanded clay and sand & biochar filters during decane biodegradation. In sand filters, decane was biodegraded more slowly and hydrogen isotope fractionation was visible. Still, the range of observed apparent kinetic hydrogen isotope effects (AKIEH = 1.072–1.500) and apparent decane biodegradation rates (k = − 0.017 to − 0.067 day−1) of the sand filter were low. To conclude, low biodegradation rates, small hydrogen isotope fractionation, zero order mineralization kinetics and lack of microbial biomass growth indicated that mass transfer controlled biodegradation.

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